Wirebonds have been used for many years to provide electrical signal connections from one integrated circuit to another. In conventional electronic circuit arrangements, there are often a large number of signals that are passed between signals.
In the field of opto-electronics, wirebond connections may also be used to create the data signal path from an electronic integrated circuit to an opto-electronic subassembly. FIG. 1 is a simplified diagram of this arrangement, illustrating an interconnected opto-electronic subassembly 10 and electronic IC 20. In this case, a pair of wirebonds 30, 32 is used to provide a digital data signal and its complement (hereinafter referred to as DATA and DATA), generated on electronic IC 20, as a signal pair to opto-electronic subassembly 10, where this signal pair may thereafter be used, in this case, to control the operation of an optical modulator (not shown). FIG. 2 is top view of this prior art arrangement.
It has been found that wirebond connections do not perform well at very high data and/or symbol rates (for example, in excess of 10 GHz). Indeed, the imaginary impedance Z of a wirebond connection can be on the order of j62Ω for a data rate of 10 GHz, whereZ=j2π*f*L. In this example, L (inductance) has a value of approximately 1 nH for a wirebond having a length of about 1 mm and a diameter of 25 μm. As operational speeds increase, it is clear that the higher values of the imaginary impedance will ultimately limit the operating speed of the device.
One solution to this problem is to eliminate the use of wirebonds, and instead connect the IC to the opto-electronic subassembly using the well-known “flip chip” arrangement. In this case, IC 20 would be “flipped over” and mounted face-to-face on the top surface of opto-electronic subassembly 10. Inasmuch as many opto-electronic subassemblies can generate substantial amounts of heat, the use of flip-chip arrangements is not considered practical in all cases. There may be other problems associated with using a flip-chip method.
As a result, there is a continuing need to provide an improved configuration for interconnecting an electronic integrated circuit and an opto-electronic integrated circuit, particularly as data rates continue to increase.